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New rating system for sound insulation in buildings


The harmonization of European standards initiated in the middle of the eighties of the last century also concerned sound insulation in buildings. The aim of the harmonization was to measure and to evaluate - throughout Europe - building elements and buildings in accordance with uniform standards to facilitate transnational trade and activities.

As the respective standardization bodies are, however, composed of experts who have no political authority to make decisions, the result of the harmonisation was that practically all existing measurement and evaluation quantities were combined in one standard. In the now upcoming revision of the central evaluation standard ISO 717 "Rating of sound insulation in buildings and of building elements", an essential ”slimming” of the evaluation quantities available for the noise protection in buildings has, therefore, been tackled whereby also historically grown inconsequences were to be corrected. The draft of the new ISO 717 presented here has been revised by the two chairs of the relevant standards working groups, Prof. Dr. Judith Lang, Vienna, and Prof. Dr. W. Scholl from PTB Braunschweig.

For the determination of the sound insulation ability of a building element by means of one single numerical value (the so-called "single-number value"), quite different procedures can be applied. It is, for example, possible to expose the building element to a specific noise - for example to a typical traffic noise - and to investigate the transmitted sound with respect to its loudness, its audibility, or to what extent it is annoying. If the noise were human speech, an evaluation of the intelligibility would, in addition, come into question. From these transmitted sound events, corresponding characteristic values can be formed - among others the so-called "A sound level", for which the different frequency components of the noise are assessed analogous to the sensitivity of the human hearing and then energetically summarized. The so-called "evaluated sound insulation indices" are based on quite a different kind of evaluation. Here, the ratio of incident sound power to transmitted sound power is represented as a frequency spectrum and compared to a kind of ideal curve ("reference curve") which is shifted in such a way that the curve of the building element to be evaluated is, on average, lower by 2 dB at the most. The value of the ideal curve at 500 Hz is then the single-number value for the building element.

Detailed investigations which have been carried out recently by Park, Bradley and Gover and by Mortensen have shown that the highest correlation exists between the subjective evaluations and the single-number values which are based on A-rated sound level differences. This is why the proposal for the new ISO 717 now only contains three of such airborne sound reduction indices:
- Rtraffic as the sound reduction index for traffic noise,
- Rliving as the sound reduction index for "living noise" coming from the neighbour, and
- Rspeech as an index for speech privacy.

The investigations stated above also recommend letting the observed frequency range of the two first-mentioned indices start already at 50 Hz.

In the case of the so-called "impact sound", it is also planned to replace the reference curve comparison by the hearing-orientated "A-rating" starting at 50 Hz, especially with respect to walking noise in the buildings. What is new is the change from the impact sound levels which have been used so far as characteristic values to newly defined impact sound insulation indices. In this way, airborne sound and impact sound can be treated completely analogously and the possibility of investigating sound insulation with respect to different excitation spectra then also exists for impact sound.

At present, the proposed system is being dealt with as a draft standard at the ISO level and will then be submitted to the member states for voting on.

Contact person:

Werner Scholl, Dept. 1.7, Email: Werner.Scholl@ptb.de